Right now my favorite lights are the Cygolite Hotshot, the Knog Blinder 4V and the Serfas Shield.

However, the Serfas Shield that I got was NOT waterproof. Serfas is replacing it for me, so I assume it's SUPPOSED to be waterproof, but at least one was not.

The Hotshot is waterproof, as is the Knog.

The mounting system on the Knog is simple but not flexible. You need a seat post or similar tube to strap to, no options. Also some have said that it breaks easily. It's a light that I like though.

I will note that these new, high power tail lights don't last as long on a charge as the Superflash. The Knog dies pretty fast, the Serfas too (not surprising, they're both stupid bright and you gotta pay for that somehow). The Hotshot seems to last longer but that's probably because it has flash modes that have the light on for less time per blink. Also it's not quite as bright as the other two.